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S&S Swan General - 40 Star Swan, Fuel leakage - Please help!
21 January 2022 - 20:48
Join Date: 09 November 2021
Posts: 43

40 Star Swan, Fuel leakage - Please help!

Hi all, I am a new proud owner of a swan 40 that was in Cagliari (Sardinia). Without knowing the boat properly as soon as I put the boat on the water (with a few days before as a preparation) I reckless crossed the med and I am now on my way to Portugal. I was amazed how well and easy it all went with the Swan. No incidentes excpt a leakage from the fuel tank.

I know the leakage came either from the tube conecting the inlet (on the cockpit floor) or the cover (that has a gasket) on the top of the fuel tank that is bolted wity many screws. I know this as there was diesel on the top of the fuel tank. A third and long shot possibility can be from the fuel tank vent that is also on the top of the tank.

My questions are:

Is it normal for the gasket to be worn out and if so any sugestions on how to replace?

Is it possible that the cause can be the fuel vent to be obstructed?

I still did not check the tube as now I am not near the boat. But i think this will be easy to do and fix.

Help is apreciated. Many thanks!



Star Swan

Swan 40/047


22 January 2022 - 10:29
Join Date: 05 August 2010
Posts: 164

Dear Duarte,

congratulations to your Swan! I did the same, bought the boat that had been standing on the hard and started sailing. I have not regretted it, yet would not do it that way again.

I attach a picture of the top side of the fuel tank taken on our boat, and as you can see, we had a small leakage as well. All of the parts that can cause your leak are visible. That includes the top side of the tank, of course; if you have a small hole, fuel can leak when the boat is heeling and fuel sloshing inside; otherwise gravity will prevent leaks, and your finding of fuel on the top of the tank certainly cannot be explained by a hole on the bottom.
You can see most of the removable inspection cover (bolted down with a lot of bolts) with a central bolt. The central bolt is opened to insert the fuel indicator rod to check how much fuel is left, though once you get to know your engine and keep track of the motor hours, you will have a very accurate estimate anyhow. The central bolt has a metal washer used as gasket.
The inspection cover has a rubber gasket with holes for all the bolts. Ours is still tight and not worn (as it is not exposed to sunlight nor to a lot of movement, there is not a lot of wear but ageing), but it would be easily replaceable with a fuel-resistant rubber.

The topmost of the three tubes exiting the tank is the vent line, being continued as a black plastic tube leading aft and exiting the boat near the stern. At the time we took the picture, we had already loosened the hose clamp; as you can imagine, an untight clamp can lead to leakage, but I would not expect a lot of it; same reason as for the top side of the tank.

The middle tube is the return flow of the diesel engine (we had an additional fuel tank connected by electrical pump; that is the branch on the return flow line). The last tube is the diesel line to the engine. All of the tube clamps on the connectors, of course, can be leaking but are easy to replace, as well as the connectors themselves. The former owner obviously cared less about using fuel-resistant tubes.

All three tubes are stainless steel welded into the inspection cover. If you remove the cover, you will see that (logically) only the diesel line reaches down to the bottom of the tank, so the tubes are not interchangeable.
We had a small leakage problem on a rather unlikely spot - the entry of the return line (which is welded from the lower side). I sealed it with a thickened epoxi variant that allows for very small movement (called G-Flex) which I applied with a toothpick to reach the part under the inlet.

You can clean the top side of the tank and run the engine for a while in port. Check for leaks. If the leak appears (i.e., you find fuel on top of the tank) the problem is in one of the two diesel lines.
Otherwise, take the boat sailing, but after stopping the engine, clean the top side of the tank. If your leak appears when you sail and heel but you are not using the engine, check the gaskets. I'd suggest placing kitchen paper at the critical points; you can easily spot the leaks then.

Hope that helps.

Fair winds,
Martin (Vellamo, 48/039)


top side of fuel tank

22 January 2022 - 16:33
Join Date: 03 March 2007
Posts: 241

Hi Duarte


I also had a leak but it was from the fill tube on the top of the tank.. The filler cap assembly is attached to a tube/nosslecoming up from the tank with a piece of hose.  If the hose is acidentally hit with gear etc the tube on top of the tank will crack.. This will allow fuel to leak onto the top of the tank.  Leak is worst when the tank is full. I  suggest cleaning the top of the tank off and having someone fill the tank with fuel while you watch for a leak..  Before this option take the hose off and see if there is a crack in the tube on top of the tank.. If you push the tube SLIGHTLY you might see a minor crack there...  I use a forehead lantern in that area, not much space.  If this is the case what I did was sand the tube and top of the tank.. wipe down with acetone and then apply two layers of biaxel fiberglass mat on the tube and region around the tube on the tank... 

Problem solved...

At one point I wanted to clean the tank and tried to remove the fitting with many bolts... I  gave up and cut a new access hole.. I have not heard of this seal breaking down but then it is over 50 years old. I hope you do not have to tackle this!!

Again the friend filling the tank with you watching will solve it... Be sure to put paper towel down to help you pinpoint the leak...


As far as taking chances... I sailed my girl a few times in the Chesapeake after I did a 2 year restoration and then proceeded to single hand back to Europe. Learned a lot about her and me on that trip.  I swore I would never sell her after that trip.  She and I spent 3 days is a Beaufort 10  seven hundred miles NE of Bermuda.. That is the kind of boat you bought!!!!!

Always here to answer those questions I can.. but Lars is the MAN!!!

Fair winds


22 January 2022 - 17:02
Join Date: 02 January 2008
Posts: 1547

Dear all

Very quick answers!

An additional comment - washing with vinegar removes the diesel smell
Kind regards

23 January 2022 - 08:05
Join Date: 03 March 2007
Posts: 241

Thanks Lars,


Always nice to learn something new!!!


Fair Winds




23 January 2022 - 12:18
Join Date: 09 November 2021
Posts: 43

Dear Martin,


Thank you so much for taking so much time in detailing the system and explaining me solutions. It is a fantastic reply that I relly apreciate.

My system on the swan 40 is slightly diferente than your beautifil swan 48, nevertheless it will be of big help once I attack the proplem. Unfortunatly I am not in my boat and only will be next tuesday in Alicante. It was very stupid of me not taking photos.

I will be back to you as soon as I fix the problem.


Fair winds!


P.S. I saw two 48 to buy, Windy (036) and Hush of liminghton. But they were a little to much for my wallet and for my single handed situation as my son is only 10 yet! 

23 January 2022 - 12:21
Join Date: 09 November 2021
Posts: 43

Hi Mike,


Thank you so much again for such help and smart advices. You have your boat for many years and I just staring to know mine. I will follow your advice and will try to find the problem. Last thing I will attack if I do not fix the proble is to unbolt the inpspection cover. 

I do not have picture now as I am not in the boat. Next tuesday I will and will share some photos with you.


Thank you so much again!!



23 January 2022 - 12:22
Join Date: 09 November 2021
Posts: 43

Dear Lars,


What a great advice. I guess I will buy a few litters (gallons even) of Vinegar!!!


Thank you so much! Have a nice weekend!




02 February 2022 - 02:34
Join Date: 31 July 2007
Posts: 88

Hello All: My Swan is 040/12 and after I bought her in 1991 I removed the lid of the fuel tank and found the seal between the lid and the flange crumbling. Most of the seal was in he bottom of the fuel tank. Of course it leaked when the tank was fairly full and the boat gets tossed around. I cleaned everything and used a fuel resistant sealant to re-install the cover. There are many studs on the flange and as I remember, I broke off one. The bottom of the tank is the hull and the suction tube is about 6 inches from the bottom. As a result it will suck air before the tank is completely empty. Happened to me. I thought I could make it to a marina but had to sail in. Then had to bleed the engine after filling the tank. I made a stick to sound the fuel level by way of the fuel filler in the cockpit and marked the stick. Maybe this information is helpful!   

These are wonderful boats with a very comfortable motion at sea and go to windward without pounding even when the wind is against the current. We have even raced the boat and found that with a clean bottom she was much faster than other boats. I don't know why. In a Spring Series regatta we were so far ahead that we lost sight of the following boats

Pete Lange CYGNUS


11 February 2022 - 19:14
Join Date: 09 November 2021
Posts: 43

Dear All,

Thank you again all for you nice comments and reports on swan 40. Your experience is so valuable for someone without like me.

So I believe I discovered the leak and unfortunately is coming from the inspection cover gasket, because is worn-out, or just because the vent tube is blocked (I think...) as when I am filling up the tank I hear air coming out of the inspection cover gasket and maybe it forces the diesel coming out through the gasket. On the photo, between the two back bolts there is bump on the cover. Hard to see I know.

So my idea is to put, as quick fix, a silicon sealant diesel resistant and once at home Ill make a special gasket. Obviously, I will try to unblock the vent tube.

 Question: Any advice on the gaskets?


18 February 2022 - 18:02
Join Date: 03 March 2007
Posts: 241

Interesting!!! your inspection plate has S&S bolts i guess threading into the tank. Mine has studs with nuts on them. and many of them  Yours is MUCH easier to access as in my case the nuts are 1/2 thickness and it is very difficult to get a wrench on them.  I avoid silicon because it is a pain to get paint to stick if you try to refinish after using it.. But maybe that is just me.   I do not have any on the boat...






18 February 2022 - 18:57
Join Date: 31 July 2007
Posts: 88

I remember years ago that, I believe Lars Strom, said that silicone sealant was prohibited at the Nautor Swan workshops to even have around because of the chance that any of the stuff might get into the laminate and result in poor adhesion. Lars - please correct me if my memory deceives me. In my own opinion, 5200 type of sealants are much better, they form a strong bond and - please verify this - are fuel restistant. I used many gallons of it because it was Boeing surplus, out-dated and cheap when I built my own boat. I did see with my own eyes that Boeing used it as fuel tank sealant. Once you use silicone type sealant and it has cured, it is almost impossible to remove. You have to discard the pieces it was used on.

19 February 2022 - 11:21
Join Date: 02 January 2008
Posts: 1547

Very long ago the yard used silicone based deck mastic, It was then found out that silicone was everywhere in the factory, effectively distributed by the shoes of people walking on the decks and then around the shops.
It is impossible to re-varnsh a table treated with Johnson's Pled, containing silicone
Kind regards

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